Speculative Evolution Wiki:Competitions/Comp. 2: Aquatic Supremacy/Scarabaeocancri
It's the dawn of a new era, one where our familiar tetrapod fauna is not dominant, and at great risk of going extinct within the next 100 million years. An asteroid has plunged into the Earth, and wiped out 70% of all animal species. But tetrapods were hit much harder, with an extinction rate of over 90%. Their diversity plummeted from 23,000 species beforehand to 2000 species afterwards. A tetrapod dynasty had flourished for more than 450 million years before, and now after the transfer of power from the first amphibians to the anapsids; and then to synapsids, archosaurs, mammals, and squamates; no tetrapods could inherit the Earth any longer. And for the first time in history, insects have truly conquered the both land and the ocean. They at last replace their probable ancestors, the crustaceans. Many crustaceans are in danger of going extinct by competition from a new group of scarab beetles – the Scarabaeocancri. Evolution The Scarabaeocancri are unique among hexapods, in that at least the derived Neocancri can manage to stay underwater for an infinite amount of time. Normally, an insect dies within a minute of touching water, while even aquatic insects cannot dive for long. But in the age of insect domination, one group managed to both degenerate and become the most successful aquatic arthropods since the trilobites. Now, surely insects still retain the ability to live in water from their crustacean ancestors, yet none have but the Scarabaeocancri. But this story of evolution begins long before even the first of this group. We begin with the humble scarab beetle Aphodius. Aphodius is none other than a small scarab beetle, in fact the larger species of this genus reach only just above a centimeter in length. And to go from this diminutive, unimportant beetle to conquerers of the ocean is a long path of evolution, but this was the destiny of Aphodius. A series of ordinary aphodiine beetles descended from Aphodius, that is, until the world froze over. A major glaciation pushed the beetle in several directions. A need to use less energy became apparent, and eventually those with mutated fused elytra fared better. This early step towards the Scarabaeocancri was known as Ankylopteryx, meaning "fused wing". This was the only step in the evolution of Scarabaeocancri which was apparently unrelated to the conquering of the ocean, yet was still a vital step. By the time the fused elytra characteristic of Ankylopteryx had evolved, the glaciation was over. It seemed that this short-lived advantage would kill the species, and this strange and unique beetle was an evolutionary dead end. Many strange side branches evolved, and the vast majority stayed far from water, such as a North American desert group which burrowed underground, thus keeping wings useless. The majority of the evolution of this group in fact happened in North America, and since the glaciation, this harsh desert would be the last place one would expect an aquatic insect group to evolve. North America was indeed not their native habitat (being possibly introduced, as one Aphodius species is, as opposed to naturally migrating to North America), but these changes in the climate of the continent continued to keep this branch of scarabs on par with other beetles. Finally, 94 million years in the future, the first of the true Scarabaeocancri evolved, Apteraphodius, the first to lack rear wings under its fused elytra. This apparently was simply to conserve resources. It was also semiaquatic, diving down in air bubbles, usually to get food, in this case algae and zooplankton. It appears to have been pushed by the dry climate and sparse food to live on the coastline, the only place in all of North America which is not a cold desert. Still limited in size in the relatively low oxygen atmosphere, this 1.5 centimeter genus was far from the titans to come. By 105 million years in the future, the crown group Scarabaeocancri had evolved, the Sinebranchiinae, a group lacking true gills, having only intermediate tracheal tube/gill structures; and the Neocancri, a group of true aquatic insects with crustacean-like gills. Unlike all other aquatic insects, the Neocancri maximise the oxygen they can get underwater by completely losing the tracheal tubes during larval development (during which they are only semiaquatic) and absorbing oxygen from the water through their feathery gills, and exchanging oxygen in their blood in fish gill-like structures, thus putting them almost on par with vertebrates in efficiency of respiration. Anatomy In general, the external anatomy of Scarabaeocancri is the same as scarab beetles. The main differences in external anatomy are the aforementioned fused elytra, stockier legs to help support the pressure of the water, vestigial antennae, and gills. The vestigial antennae evolved because faced with underwater pressure, the antennae would break off. Instead, these vestigial antennae are connected to an internal organ called the cephaloreceptor. This organ amplifies the electrical signals which pass through the vestigial antennae, then sends them via nervous pathways to the brain, where they are processed as touch and smell. Internally, the three main differences in anatomy from typical scarabs are the cephaloreceptor, the unique respiratory organ which is a rudimentary version of fish respiration, and the lack of rear wings. The respiratory organ is a single fish gill-like structure which circulates blood and contains the capillaries. This lies on the inside of the thorax, usually on one side or the other. However, the external part of the respiratory organ is more of a crustacean gill-like structure, being dense and feathery. The gills are usually concealed by a flap on either side of the thorax. Although the internal respiratory organ is asymmetric, the crustacean-like feathery structures are on both sides, thus obviously doubling the oxygen take in. These characteristics are almost exclusive to the Neocancri, and the Sinebranchiinae lack the stockier legs, vestigial antennae, cephaloreceptor, fish-like respiratory organ, and to some extent the crustacean gill-like structures. This subfamily can only stay underwater for short dives, and can only filter in enough oxygen underwater to stay alive from about 30 seconds to five minutes. However, the Neocancri can filter in enough oxygen through their combination of respiratory strategies to not only live their entire adult lives underwater; but also allows them to grow to gigantic sizes, one of the largest of any aquatic arthropod in history, and having one of the largest impacts on marine communities in all of history. Groups The Scarabaeocancri are divided into four subfamilies, each with a unique way of life. Many of the early members of the group were not categorised into any of these subfamilies, but by 114 million years in the future, only those in the four major subgroups remained. Sinebranchiinae The Sinebranchiinae are a basal group of Scarabaeocancri, and monophyletically defined as everything closer to Sinebranchia than to Scarabaeocancer. No species is fully aquatic, but certain ones are more aquatic than others. This group is exclusive to the western coast of North America, and the closing Pacific Ocean is their largest problem. At half the size of today's Atlantic, the Pacific Ocean closes approximately 165 million years in the future. The first of the Sinebranchiinae evolved 105 million years in the future, the type genus Sinebranchia. Having only minimal gills, Sinebranchia was dependent on the air bubble strategy of certain aquatic beetle of the present. Throughout their history, 57 genera of this subfamily existed. The longest lived and most prolific genus was Branchiodiplocaulis, accumulating 108 species during its lifetime of 112 to 136 MyF. This genus had intermediate gills, and was one of the closest to be fully aquatic of this subfamily. The last of this subfamily died out 138 MyF, when the Pacific Ocean started to become trapped, and the coastal swamps and central deserts of North America disappeared. The last genus, Plutonis, lived in the underground reaches of the swamp for most of their life, avoiding the conquering rainforests and high oxygen of the continent which brought about the age of terrestrial arthropods. With their strange intermediate respiration, they were easily outcompeted by many other giant beetles which took advantage of the high atmospheric oxygen rather than the minimal oceanic oxygen, in an equally minimal ocean. Neocancri Benthoaphodiinae Considered to be the most successful of the Scarabaeocancri, the Benthoaphodiinae are six centimeter long fully aquatic scarabs with an appearance similar to their ancestor of the present day, Aphodius. The first subfamily of the group to become fully aquatic, the Benthoaphodiinae split off from the rest of the Neocancri (the gill-bearing, fully aquatic group) immediately after the extinction marking the end of tetrapod rule for the rest of history, 110 MyF. They were the "first pioneers" of the arthropod ruled world. The Benthoaphodiinae took few evolutionary risks after the great achievement of conquering the ocean. They kept a low trophic level (their diet consisting entirely of plankton and algae) so they were not dependent on the very unstable ocean of the time. The largest of the group (Gigantoaphodius) measured ten centimeters, and even that was apparently far too large to be safe. Gigantoaphodius evolved 126 MyF, and went extinct only two million years after it evolved. Also, the exoskeleton hardened, meaning three things critical to the group's survival: *They were "not allowed" to grow any larger than Gigantoaphodius, or they would be crushed. *They were not as susceptible to predators as the Titanoscarbaeinae, which did exactly the opposite: evolved a lighter exoskeleton to grow larger. *Deep underwater, the rigid exoskeleton would not be broken to due the pressure. Over their lifetime, the Benthoaphodiinae evolved into 196 genera, the most by far of any group of Scarabaeocancri. The type genus, Benthoaphodius, is notable for living deeper than any known insect, but their most successful genus was likely Pelagiaphodius. Despite its name, it was not pelagic, but had a habit of swimming (near the seafloor) away from predators, using strange fin-like limbs. Only two species of this genus ever existed, but they survived right up until the end of the existence of Scarabaeocancri, in an event known as or Middle Melacene faunal turnover. This event brought a demise to the last remaining genera of the group, including twenty or so genera of Benthoaphodiinae; and the last remaining genus not of the subfamily, the eponymous Scarabaeocancer. Deinocancri Titanoscarabaeinae The Titanoscarabaeinae are by far the largest beetles in history. Despite their apparent ferocity for such an insect, they are completely herbivorous, but fearsome nonetheless. Members of a group known as the Deinocancri, they are the sister taxon to the Scarabaeocancrinae. They first evolved 117 MyF, their first member being the benthoaphodiine-like Inarmatus. Its name is ironic, being perhaps the best armoured of the subfamily. However, the robust look and large size of later members make this look like the "weakling" of the group. By 126 MyF, natural selection had caused all Inarmatus-like to go extinct, to be replaced by the Titanoscarabaeini of their own subfamily, the group of titanic beetles this subfamily is usually associated with; but their niche to be replaced entirely with the diversifying Benthoaphodiinae. The thin exoskeleton characterising the later members of this group led to many members living in shallow water. While Benthoaphodius could live 900 meters below the surface (and had no problem doing so), the pressure meant that only those with a thick exoskeleton (perfectly exemplified by the Benthoaphodiinae) could live this far down. No titanoscarabaeine ever went deeper than 100 meters. Another ironically named titanoscarabaeine, Armatocancer was the first and most successful of the Titanoscarabaeini. Weighing a massive 300 grams, over three times heavier than any living beetle, its thin exoskeleton compromised between having to deal with the pressure of its somewhat deep habitats and being able to scare off any predators it happened to encounter. First evolving 122 MyF, it survived until 135 MyF, but was the last of its kind. Meanwhile, larger titans were evolving. The group's namesake, Titanoscarabaeus, was about the same weight as Armatocancer, but impressively, could reach relatively high speeds underwater, and was a fiercely territorial, arm-locking giant. The majority of the tribe stayed similar to Armatocancer, although the exception of Titanoscarabaeus was not alone. Living a short and brutal life, perhaps the most so of any beetle, was Eugoliathus, a 600 gram giant with an exceptionally thin exoskeleton, and the largest insect in the history of the Earth, beating the giant Carboniferous dragonfly relatives in the order Meganisoptera by 100 grams. But its first appearance 129 MyF was practically its last, with new predatory arachnids of the seafloor killing it off within 1 million years, and setting impending doom for the remaining genera. These remaining genera numbered only 13, but made up a fair percentage of the 24 ever in existence, counting those not of the tribe Titanoscarabaeini. Titanoscarabaeus may have been able to run, but its large size and thin exoskeleton didn't quite pay off, the genus going extinct by 133 MyF. The first and last of the tribe, Armatocancer, had finally died off as well two million years later. This was the first stage of the Middle Melacene faunal turnover. Scarabaeocancrinae Scarabaeocancrinae is a subfamily containing the last vestiges of the Early Melacene fauna, and the last remaining insects occupying a niche which was to be taken by other arthropods. This subfamily contained the most populous and dangerous marine predators of its epoch, and by the Middle Melacene, they still hung on. Their evolutionary strategy was to become strong, and to be apex predators. In a brutal, unstable ocean, this was hard, but the first of the group, Deinognathus, somehow had already achieved this. And apparent ghost lineage had existed for nine million years, because Deinognathus seemed to be highly derived and appeared nine million years after the sister taxon to its subfamily, Titanoscarabaeinae. Its mandibles were already similar to those of Scarabaeocancer, as illustrated, and could puncture a huge wound in most invertebrates. The long legs, however, had yet to evolve, but the diet was also similar. Echinoderms and crustaceans made up the majority of its diet, but the fish that only more derived genera could prey on were absent from its diet. The size was only slightly larger than most Benthoaphodiinae, at eight centimeters. Four million years later, they had reached the Atlantic and Southern Oceans and were composed of 17 genera. While Titanoscarabaeinae and Sinebranchiinae never reached any ocean other than the Pacific, Benthoaphodiinae and Scarabaeocancrinae did not remain trapped. Benthoaphodiinae had a near worldwide range at its peak diversity, and in most places Benthoaphodiinae travelled, Scarabaeocancrinae followed. It seems that the strong and fast mandibles were made to crush any sort of exoskeleton, and in later genera it seemed convenient to eat their kin, the completely herbivorous benthoaphodiines. The type genus, Scarabaeocancer, had evolved by 140 MyF, and it, like other members of the subfamily, had evolved the characteristic long legs and partially piscivorous diet of the Scarabaeocancrini tribe. While exoskeletons, especially those of sea urchins, were very tough, and animals with exoskeletons made up the majority of its diet, fish actually seemed to be easier to hunt. Not only were the tetrapods declining, the fish were as well, but still contained 20,000 species. Large predatory fish were nearly gone, even the perciform Carcharomimidae, which had persisted through the first 20 million years of the Melacene. The remaining fish were typical small herbivorous fish of the seafloor. Scarabaeocancer could be described as a crab insect, hence its name. Hunting smaller prey, it used its long legs like a spider to contain its victims. In fact, these arachnid-like abilities allowed it to persist and become the last of its subfamily. But 147 million years in the future, while it was one of the last four genera of Scarabaeocancri, the true arachnids had overtaken it. These were scorpions, actual sea scorpions. Ecology and Life Cycle Ecological Niche The Scarabaeocancri fit into ecological niches sometimes unique, sometimes analogous to a niche in the present or past. Sinebranchiinae are similar to modern diving beetle; they behave and look like such. Benthoaphodiinae and Titanoscarabaeinae both fit in unique ecological niches, which can by described as nothing other than herbivorous large aquatic beetles, exactly what they are. Scarabaeocancrinae are closest to predatory arachnids or crustaceans, and although their name meaning "scarab crabs" is sometimes an accurate description, perhaps the eurypterids are a closer analogy, the group having been overcome by completely eurypterid-like scorpions. As time went on, the ecological relationships of the Scarabaeocancri with other groups changed. When the Sinebranchiinae first evolved, it was near the end of the second age of reptiles, and the major predators of this group were lizards. After the extinction marking the end of this period, they had fewer predators, but in this age of insects the swamp was occupied by predatory dragonflies, which fed on beetles. The Sinebranchiinae were finally driven to extinction by a third wave of predators, arachnids, mainly spiders. The predators of the Benthoaphodiinae were minimal until the beginning part of the Middle Melacene faunal turnover. Evolving during the extinction, perhaps, they never dealt with many aquatic predators. Aquatic tetrapods had all died off during the extinction event, although smaller predatory fish were somewhat common. The predators of the Benthoaphodiinae when they first evolved therefore were restricted to small predatory fish with strong jaws. As with every other subfamily of their kind, it was arachnids which drove them to extinction. The case was much the same with Titanoscarabaeinae, however later species sometimes completely lacked predators. Scarabaeocancrinae were predators of echinoderms, fish, crustaceans, and occasionally even arachnids. With their strong bite, they usually warded off predators of their own, however, these were only arthropods, and by the first appearance of this subfamily the apex predator niche had been mostly taken from the vertebrates by cephalopods. These included octopi and squid of many diets, and the majority at least sometimes fed on predatory arthropods, including Scarabaeocancrinae. The long term advantages (the Scarabaeocancrinae preoccupied this niche) scorpions had over this group is that they had more powerful jaws, a powerful sting, and could grow larger. In the end, the aquatic arachnids persisted for the rest of the Melacene. Life Cycle and Behaviour Larva The life of all members of Scarabaeocancri starts out as a grub-like larva, semiaquatic in most species. The size of this larva is generally irrelevant to the size of the adult, and ranges from 3 to 6 cm. The metamorphosis in the larva is radically different in Sinebranchiinae and Neocancri. The larvae of Sinebranchiinae live for 4 to 6 months before metamorphosing, and during metamorphosis small growth protrude from the head, growing into gills by the end of the larval stage. Meanwhile, in the Neocancri, the differences from the Sinebranchiinae never show up before at least halfway through the larval stage. All of their evolutionary adaptions to life underwater are easily sighted during the growth period of the larva. Because of these radical changes, the larval stage lasts up to 14 months, three times as long as the average larval period in Sinebranchiinae. There are, however, certain exceptions to this general rule. The main exception is the small group of Neocancri which have fully aquatic larvae with fully developed gills, which is monophyletic, including later Benthoaphodiinae such as Benthoaphodius and Pelagiaphodius. This adaptation was expensive, but worthwhile for the most tied to water of all Scarabaeocancri. In fact, Pelagiaphodius is often considered the last remaining of the Scarabaeocancri, and this adaptation was crucial to its survival. The survival rate in larvae is extremely low for a scarab, with 300 eggs laid on average, and only 6 surviving. Certain scarabs are known to possess complete parental care, however the Scarabaeocancri are limited by their having to stay in water. The grubs are fat, and completely vulnerable to predation, only being able to hide in the places where their eggs were hidden. The survival rate is, however, much higher with the fully aquatic larva mutation, generally in this group 80 survivors out of 200 eggs, with parental care being an option, feeding their young plankton and aquatic plants. Adult Independent of the length of the larval stage, the lifespan of the adult stage is always around one year. During this period, they develop for up to six months in larger species, and females will lay eggs up to four times during this period. While this repeated laying of eggs was originally to compensate for the loss of young with inability of adults to go onto land, this strategy worked so well that it caused a population boom by the first time this evolved. The survival rate remained low, but the number of eggs laid remained much higher, and went over a reasonable limit for one population. It was this occurrence that drove the Benthoaphodiinae and Scarabaeocancrinae to other oceans. While this population boom happened in the other two subfamilies, the Sinebranchiinae were flightless and were not fully aquatic; while the Titanoscarabaeinae started with a very small population, and the boom in population never drove them to move. Interestingly, the population boom happened independently in all four lineages, saying that there was a sudden but long waited for tipping point in population. In the late Benthoaphodiinae, the population grew yet larger, as the survival rate increased far more than the egg laying rate decreased (including the eggs being laid only once, to allow parental care, feeding the young on algae, rather than dung like their ancestors). The Titanoscarabaeinae take the longest to grow after pupating, while the Benthoaphodiinae and Sinebranchiinae grow for at most one month. The four groups are nearly indistinguishable in appearance in the larval form, but in the adult form could just as well be different families. The characteristic popping out gills of Sinebranchiinae and the crushing jaws of Scarabaeocancrinae are already developed by the emergence from pupation. The main difference to happen in the adult stage is the growth, which can inhibit the amount of eggs laid as a longer growth period means less opportunities for mating, the main reason for the low population of the Titanoscarabaeinae. Most Scarabaeocancri remain peaceful when it comes to choosing mates, however, the Scarabaeocancrinae are entirely different, with the males genera like Scarabaeocancer engaging in jaw-locking fights, sometimes to the death. While from the males' point of view this rids them of rivals, from the sexually selective female point of view it shows that they have genes fit for hunting, the jaws being the only thing helping them eat hard prey like sea urchins. While this sexual selection made Scarabaeocancer more fit, the fact remains that males are never polygamous in this group, and in theory this may have led to the extinction of Scarabaeocancer, killing males and stopping the reproduction of females, and therefore leading to a small gene pool. However, this may be a false assumption, with the aforementioned better traits in scorpions. There is the story of perhaps some of the most successful beetles on the planet, first evolving from desert dwelling small dung beetles to semiaquatic diving beetles and finally to conquerers of the ocean and near-apex predators. Their downfall was, however, their unknown and unexpected competition from arachnids in a previously insect-ruled perhaps, and possible self-destruction leading to the demise of the largest known insects in history. Scarabaeocancri